pollinator-mediated speciation in angiosperms: what do we know?

Pollinator-mediated Speciation in Angiosperms:

What Do We Know?

Lecture Overview

• Vascular plant diversity

• Modes of angiosperm speciation

• Pollination modes and angiosperm diversification

• Experiments: pollinator-mediated selection on floral traits

• Conclusions

Vascular Plant Diversity

• 260,000+ species

Vascular Plant Diversity

• 260,000+ species

~ 850 gymnosperms (290 mya)

~ 9800 ferns and fern allies (400 mya)

~ 249,000 angiosperms (130 mya)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.



Rapid diversification of angiosperms: “Abominable mystery”



Rapid diversification of angiosperms: “Abominable mystery”

His attempt to identify a single cause: “wretchedly poor”

Lecture Overview





• Conclusions

Modes of Angiosperm Speciation(speciation = reproductive isolation)

Modes of Angiosperm Speciation(speciation = reproductive isolation)

• Mechanical barriers (e.g., mountain range)

Modes of Angiosperm Speciation (speciation = reproductive isolation)


• Genomic events- polyploidy (e.g., diploid to tetraploid)



• Genomic events- polyploidy (e.g., diploid to tetraploid)- chromosomal rearrangements



• Genomic events- polyploidy (e.g., diploid to tetraploid)- chromosomal rearrangements -

• Pollinator-mediated reproductive isolation- evolution of different floral morphologies

Lecture Overview





• Conclusions

Pollination Mode and Diversification

• Pollination = transfer of pollen to stigma

Anther

Stigma

Petal

Sepal



- > 99% of gymnosperm species wind-pollinated



- > 99% of gymnosperm species wind-pollinated

- > 80% of angiosperms are animal-pollinated

Pollinators and angiosperm speciation: correlations

• Angiosperm and insect diversification co-occurred

Pollinators and angiosperm speciation: correlations

• Angiosperm and insect diversification co-occurred

• Animal-pollination correlated with species richness at family level

Correlation ≠ Causation

Correlation ≠ Causation

Blood Pressure

Income

Blood Pressure

Age

Income

Age

Lecture Overview





• Conclusions

Two Important Studies

• Polemonium viscosum (alpine skypilot) and bumblebees (Galen, 1996)

Timberline 11,000 ft.

Corolla tube width = 16 mm


Alpine - 12,000 ft.




Alpine - 12,000 ft.



= 11% difference in corolla tube width


Alpine - 12,000 ft.



What explains corolla tube width difference?

= 11% difference in corolla tube width


Alpine - 12,000 ft.




Solitary bees


Alpine - 12,000 ft.




QuickTime™ and aPhoto - JPEG decompressor


Solitary bees

Bumble bees

Conclusions

• Bumblebees selected for wide corolla

• Evolution from 16mm to 18 mm corolla ~20 yrs

• Pollinator preference can cause floral trait evolution

Two Important Studies

• Polemonium viscosum (alpine skypilot) and bumblebees (Galen, 1996)

• Ipomopsis aggregata (scarlet gilia) and hummingbirds (Campbell et al., 1997)

Experiment Results

Mean corolla tube width

Visits/flower/hr.

Experiment Results


Visits/flower/hr.

Wider Flowers = More Pollen Export

Experiment Results


Visits/flower/hr.

Optical Density

More red Less red


Seed set/flower

Experiment Results


Visits/flower/hr.

Optical Density

More red Less red


Seed set/flower

Redder Flowers = More Seed

Conclusions

• Floral traits can determine level of pollinator attraction

• Pollinator preference caused plant reproductive success differences

Reproductive isolation in columbine

Aquilegia pubescensAquilegia formosa

Reproductive isolation in columbine

Aquilegia pubescensAquilegia formosa

Note - viable hybrids from hand pollination

Aquilegia pubescens Aquilegia formosa

Experimental Design (Fulton and Hodges, 1999)

Results

• Hummingbirds almost always visit A. formosa

Results

• Hummingbirds almost always visit A. formosa

• Hawkmoths always visit A. pubescens

Conclusion

• Pollinator preference based on corolla morphology resulted in reproductive isolation

Any problems with this study?


• No hybrids in array - not a complete test of pollinator preference


• No hybrids in array - not a complete test of pollinator preference

• Need to show that hybrids attract mix of pollinator types

• Are sympatric (overlapping distribution) in CA


• Viable hybrids made from hand-pollinations


• Viable hybrids made from hand-pollinations

• No hybrids seen under natural conditions

Results

0

10

20

30

40

50

60

70

80

90

M. lewisii Hybrids M.cardinalis

% of totalvisits made by bees

Conclusion

• Prove that corolla traits can determine type of pollinator attracted

• Pollinator preference can contribute to divergence of angiosperms through reproductive isolation

Lecture Overview





• Conclusions

Summary• Animal-pollination mode is correlated with diversification

of angiosperms

• Pollinator preferences can drive floral trait evolution

• Floral trait evolution in response to pollinator preferences can lead to reproductive isolation (= speciation)

• Pollinators have contributed to diversification of angiosperms

Archaeofructus

pollinator-mediated speciation in angiosperms: what do we know?

Documents

pollinatormediated speciation

pollinatormediated selection

diversification pollination

transfer of pollen

mmcorolla tube width

species richness

abominable mysteryhis

bumblebees galen